This invention relates to apparatus to stress a shank part of a fastener such as a bolt, shaft, or a stud, and more particularly to providing a plurality of jack bolts arranged at spaced-apart locations to extend between a surface of a support and an outer peripheral part of a flange for stressing the fastener through torque applied to the various jack bolts. The flange can be an integral part of the shank or the flange can be retained on the shank by, for example, threads, any of numerous forms of a retainer ring or a fastener. The apparatus of the present invention can be used, for example, to clamp arbors against opposite sides of a roll sleeve to form a roll assembly.
It is a common practice for workmen to stress a bolt by applying torque to the bolt head to advance a threaded portion along threads in a tapped hole or a nut member so that the shank portion of the bolt is placed under a desired or predetermined mechanical stress. The stress imparted to the shank portion of the bolt can be determined by using a torque wrench to measure the torque applied to the bolt or by using other means to measure the applied force by a spanner wrench. The torque may be applied to the head portion of the bolt or to the nut. A stud can be stressed in a similar way by torque applied to a nut engaged with a threaded portion of the stud. The present invention is designed to permit stressing of a large fastener, e.g., a bolt or a stud, having a diameter generally one inch or larger. The magnitude of stress that can be applied to a bolt, stud or similar fastener has limits of practicality, particularly with respect to workmen. A one-inch diameter threaded bolt made of high-strength material can be tightened by the use of a spanner wrench to the elastic limit of the material. With coarse threads, a stress to the elastic limit of the material requires about 1000 ft-lb of torque, i.e. 100 pounds of force applied by a 10 foot lever. Under ordinary condition, this exceeds the practical length of the lever and the amount of force a workman can deliver to the lever. Under usual conditions, a workman using a spanner wrench cannot stress the shank of a nut and bolt assembly that is four inches in diameter with coarse threads to 57,000 ft-lb which is the required torque to stress the bolt to the elastic limit of a typical material comprising the nut and bolt. To develop torque of this magnitude, 5700 pounds of force must be applied to a 10-foot long lever which cannot be accomplished without employing massive machinery or special facilities.
Hydraulically-powered devices are known in the art for stressing or tensioning the shank portion of a fastener but such devices are undesirable because the magnitude of force which can be developed is restricted to available mounting space for the device. If space is available for mounting a hydraulic tensioning device, it is typically necessary to develop a hydraulic pressure of about 15,000 psi. Examples of such hydraulic tensioning devices can be found in U.S. Pat. Nos. 3,835,523; 3,841,193; 3,886,707; 4,075,923 and 4,182,215.
Thermal shrinkage is a much older method for stressing a bolt. The bolt is first heated to elongate its shank. The bolt is then torqued to a precalculated stress and finally the bolt is allowed to cool so that upon cooling, thermal shrinkage tensions the bolt. Usually, this method cannot be used where the amount of stress must be accurately controlled or precisely established. It is also difficult to unscrew the bolt from the threaded member without reheating the bolt.